The present invention relates to impact attenuators for vehicles that have left the roadway, and in particular to such attenuators that are well adapted to bring an axially impacting vehicle to a safe stop and to redirect a laterally impacting vehicle that strikes the side of the attenuator.
Carney U.S. Pat. Nos. 4,645,375 and 5,011,326 disclose two stationary impact attenuation systems. Both rely on an array of vertically oriented metal cylinders. In the ""375 patent, compression elements 54 are arranged in selected cylinders transverse to the longitudinal axis of the array. In the ""326 patent, the cylinders are guided in longitudinal movement by cables extending alongside the cylinders on both outer faces of the array. The individual cylinders are guided along the cables by eye-bolts or U-bolts.
Stephens U.S. patent application Ser. No. 09/753,476, assigned to the assignee of the present invention and hereby incorporated by reference in its entirety, discloses an improved impact attenuator that redirects vehicles impacting the side of the barrier, and that is more easily restored to working condition after an impact. The disclosed system includes an array of resilient, self-restoring tubes. Each of the tubes is braced by a respective compression element that braces the tube against compression along a respective compression axis, while allowing the tube to be resiliently compressed transverse to this compression axis.
In the preferred embodiments described in the Stephens application, the compression element is oriented at an acute angle with respect to the longitudinal axis of the array. In an axial impact, the tubes are both collapsed along the axial direction and twisted as the compression elements are reoriented perpendicular to the longitudinal direction. The associated stresses can on occasion bend the fasteners that secure the compression elements to the tubes, which may complicate the process of restoring the impact attenuator for reuse after an impact.
A need presently exists for an improved energy absorbing assembly of the type including a tube and an internal compression element that is less subject to this disadvantage.
By way of introduction, the energy absorbing assemblies described below include a resilient, self-restoring tube, a compression element positioned inside the tube to brace the tube against compression along a compression axis, and a hinge including a first portion secured to the tube, a second portion secured to the compression element, and a hinge portion interconnecting the first and second portions. The hinge allows movement of the compression element relative to the tube when the tube is collapsed along a crush axis. This reduces bending forces on the associated fasteners and substantially reduces or eliminates the incidence of bent fasteners.
One preferred embodiment described below uses a living hinge formed of a strip of the same polymeric material as that used to form the tube. Such a living hinge provides the advantage that the compression element is automatically biased back to its original position once the array has been restored to its original configuration after an impact.
The foregoing paragraph has been provided by way of general introduction, and it should not be used to narrow the scope of the following claims.